Semiconductor laser diodes have found applications in a wide variety of information handling systems because of their compact size and because their technology is compatible with that of associated electronic circuitry and other electro-optical elements such as mirrors. They are used, among others, in data communication, optical storage and optical beam printing.
Efforts aiming at improved performance in applications requiring more than one light source have led to the design of integrated laser arrays capable of emitting a plurality of closely spaced laser beams. In general, they are used to replace slower serial operations by faster parallel processing, e.g., byte-processing instead of bit-by-bit processing, or in document scanning and printing.
A wide variety of laser array structures have been described, some of which are listed herein below:
"Experimental and Analytic Studies of Coupled Multiple Stripe Diode Lasers" by D. R. Scifres et al. (IEEE Journal of Quantum Electronics, Vol. QE-15, No. 9, September 1979, pages 917-922).
U.S. Pat. No. 4,069,463 "Injection Laser Array" (issued January 1978).
European Patent Application 0 226 445, "Laser Array" (published June 24, 1987).
European Patent Application 0 301 818, "Semiconductor Laser Array Device" (published Feb. 1, 1989).
European Patent Application 0 301 846, "Semiconductor Laser Array Apparatus" (published Feb. 1, 1989).
In spite of substantial progress made in recent years to develop a process to minimize device dimensions, further reduction in the spacing between individual beams is still highly desirable for high resolution applications. One approach consists of using optical systems to bring laser beams closer together. However, the use of individual lens systems for each beam makes such arrangement highly complex and prohibitively expensive. In addition, devices that require dimensions on the order of microns have seen their optical systems attain their physical limits. The laser arrangement described hereinbelow points to a new direction.
In addition to efforts aimed at achieving closely spaced beams, new developments have mainly focused on designs of surface emitting lasers. Therein, beams emitted in a plane parallel to the wafer surface on which the laser structure is epitaxially grown are reflected at an integrated mirror to exit the device in a direction perpendicular to the wafer surface. Such arrangements have been disclosed in the following references:
U.S. Pat. No. 3,996,492, "Two-Dimensional Integrated Injection Laser Array" (issued Dec. 7, 1976).
U.S. Pat. No. 3,996,528, "Folded Cavity Injection Laser" (issued Dec. 7, 1976).
U.S. Pat. Application 264,422, "Integrated Laser Arrays and Support Circuits" (filed Oct. 31, 1988).
IBM Technical Disclosure Bulletin, "Vertically Emitting Laser with Integrated NAM Deflector" (Vol. 32, No. 3B, August 1989, pages 498-499).
Another approach to obtain surface emitting laser diodes is described in an article "Surface Emitting Laser Diode with Bent Waveguide", by M. Ogura et al. (Appl. Phys. Lett. 50(12), Mar. 23, 1987, pages 705-707). There, a bent double heterostructure fabricated on a grooved substrate is used instead of a deflecting mirror.
However, no suggestion has been made to using optical elements that achieve the desired "surface emitting" by providing virtual sources spaced more closely together than the corresponding beam sources which can be projected by simple optical means.
With regard to the optical principle on which the present laser diode arrangement is based, similarities exist with the so-called "Fresnel's mirror" arrangement wherein light from a point source is incident on two plane mirrors mutually inclined at a small angle. Reflection at the mirrors gives raise to two virtual images. A description can be found in the handbook "Principles of Optics", Max Born & Emil Wolf, Pergamon Press, 6th Edition, page 262. This reference, however, does not in any way suggest any potential technical application of the described optical principle.